A talk page is a discussion page that you can find attached to some article and user pages. They exist for communicating with other users and discussing how to improve the wiki.
To get to a talk page from an article, just click the "discussion" or "talk page" link or button near the title of the page. To get to a talk page from a profile, just click the "Talk page" tab.
To start a new message, click the "Leave message" button at the top of the talk page.
Enter your message in the editor window. At the end of your message, type four tildes ("~~~~"). This will convert to a signature when you hit save.
Enter the title of your message in the "Subject/header" text field near the Publish button.
Click the Preview button to check your work.
Click Publish.
To respond to a talk page message, simply edit that area of the talk page, and indent your reply. You can indent by putting a colon (":") at the front of each line. Be sure to sign your response with ~~~~.
Keep your comments polite and friendly. It's always best to be civil, even if things get heated.
If any talk page gets too long, you can create an archive by typing [[/Archive]] (or any other name you like to use) onto the talk page. You can click the new link (preferably in a new window), copy over the older comments, then remove them from the main talk page.